Testing-circuit for repeaters equipped with automatic networkselectors



C. S. DEMARESR; TESTING CIRCUIT .FOR REPEATERS EQUIPPED WITH AUTOMATICNETWORK SELECTORS.

APPLICATION FILED DEC-5.1918.

v I mam?! if A TTORNEY c, s. DEMAREST. v TESTING CIRCUIT FOR REPEA'TE RSEQUIPPED WITH AUTOMATIC NETWORK SELECTORS.

APPLICATION FILED DEC-5| 1918.

1,355,897. Patented Oct. 19, 1920.

4 SHEETS-SHEET 2.

IN VEN TOR.

A TTORNEY c. s.. DEM-AREST. 1 TESTING CIRCUIT FOR REPEATERS EQUIPP EDWITH AUTOMATIC NETWORK SELECTORS.

APPLICATION HLED DEC-'51 1918:

. C. S. DEMAREST.

TESTINGCIRCUIT FDR REPEATERS EQUIPPED WITH AUTOMATIC NETWORK SELECTORS.APPLICATION FILED DEC-5,1918.

4 SHEETS-SHEET 4 .1,355,897. I Patented Oct. 19, 1920.

v INVENTOR. CJIflemare 5 A TTORNEY UNITED STATES PATENT oFFLcE- CHAR-LESS. DEMAREST, OF BROOKLYN, NEW YORK, AS SIGNOR TO AMERIGA-N; TELEr' PHONEAND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TESTING-CIRCUIT, FOR BEPEATERS EQUIPPED WITH AUTOMATIG NETWORK-SELECTORS.

Specification of Letters Patent.

Patented Oct. 19, 19-20.

Application filed December 5, 1918. Serial No. 265,429.

larly it relates to arrangements whereby the repeaters may be tested.

In order to test the efficiency of a repeater circuit a testing circuitisusually provided with which the repeater may be associated,-

said testing circuit including net works for simulating the transmissionlines with which the repeater is ordinarily used, a source of currentvariations, and a suitable indicating arrangement usually consisting ofa telephone receiver and a receiver shunt. In order to-make atransmission test, current from the source'is transmitted through thenet works and through an auxiliary circuit to the receiver, and theresultant sound observed. The current is then transmitted through thenet works and the repeater'and receiver shunt tothe receiver. Byadjusting' the receiver shunt until the same sound results as before,the transmission gain due tothe repeater may be obtained. This processinvolves disconnecting the net works from the repeater, while thecurrent is bein transmitted over the auxiliary path. g balanced bysuitable test net works associated with the repeater, the disconnectionof the line simulating net works causes the repeater to sing, and itisnow-necessary to make the repeater inoperative by opening the filamentcircuit while the testing current is being transmitted over theauxiliary path. One of the objects of this invention is to overcome thisdefect by providing an arrangement whereby auxiliary net works areassociated with the repeater when the line simulating net works aredisconnected therefrom during the testing operation.

In certain types of repeater equipment arrangements are provided wherebyartificial lines or net works suitable for balancing any giventransmission line andi s assospectively of Fig. 1

ince the net works are normally means of key 10' and conductors 11.repeater controlling key 12 is provided,

ciated equipment may be automatically selected. operation should beperformed without causing the repeater to sing and without causing anyundue inductive disturbances upon thehne. A further object of the,invention has reference 'to the provision of means in connection withthe testing circuit whereby it may be determined whether' or not theautomatic selecting apparatus is flll'lCtlOIllIlg properly. 1 In orderto accomplish this result a key is provided in con- It is desirable thatthe selecting nection with the testing equipment whereby the net workselecting apparatus may be restored to normal and then caused to gothrough the process of selecting a network anew, the test operator inthe meantime monitoring on the circuit to determine 'whether or not theoperation is performed will be apparent from the following de--scription when read in'connection with the accompanying drawing, Figures1, 2, 3"and 4 of which constitute a circuitidiagram of a preferredembodiment of the invention.

For convenience in understanding the diagram, Flg. 2 should be arrangedbelow Fig. 1, while Figs. 3 and 4 should be arranged to the left and tothe right re- The repeater equip ment of a cord circuit repeater isshown in Fig. 1 and comprises the usual amplifiers A, and A threewinding induction coils 1 and 2, input circuits 3 and 4, output circuits5 and 6 and monitoring coils 7 and. 8. The repeater ieircuit terminatesin plugs P, and P whereby the repeater. may be associated withtransmission lines such as L,- and L through the corresponding linejacks nected to a cord circuit 9 across which the operators telephoneset may be bridged bl however, and when this key is operated, the plugsP and P may be disconnected from the cord circuit 9 and connecteddirectly to the repeater equipment above described. Balancing circuits13 and 14 are connected to the repeater and associated with thesebalancing circuits as illustrated in Figs. 3' and 4 are net works N Netc., and N N etc;, for balancing the various lines J, and J Normallythe plugs P and P are conwith a pair of transmission lines and therepeater controlling key 12 is actuated, a proper combination of networks is connected to the balancing circuits 13 and 14 to balance theparticular line and associated apparatus with which the repeater isconnected. V

The testing equipment is illustrated in Fig. 2 and comprises a testingcircuit including net works N and N for simulating the characteristicsof the transmission lines with which the repeater to be tested is,ordinarily associated. The testing circuit terminates in twin plugs P Padapt- .ed to cooperate with twin jacks J and J of repeater testingtrunks '15 and 16 to which the repeater may be connected by in-.

serting plugsP and P in the jacks J and J of said trunks. A source ofcurrent var ations 16 and an operators receiver are associated with thetesting circuit and by -means of a key K, current from said source maybe transmitted through the net works N and N and the repeater to betested, to A receiver shunt,

the operators receiver. 17 is included in this path and may be usedindetermining'the gain of the repeater in the manner hereinafterdescribed. A key K is also provided and this key is so arranged thatwhen thrown to the left the testing circuit including the net works Yand.

N is disconnected from the repeater and interconnected through anaux1l1ary path 18. During this operation the receiver shunt .17 iseliminated from the circuit and auxiliary balancing net works N and Nare connected to the re eater in 'place of the net works N and l\inorder to maintain the balance of the repeater. By observing the soundheard in the receiver when the testing circuit is connected with theauxiliarypath 18 and then restoring the key K to normal sothat therepeater is again connected in the circuit the receiver shunt 17 may beadjusted until the same sound is heard as before. The loss nowintroduced by the receiver shunt is equal to the gain due to therepeater and if the receiver shunt is properly calibrated this gain maybe read directly. in terms of some suitable unit.

A key K is also provided in connection with the testing circuit which,when thrown either to the right or to the left, applies ringing currentover one end or the other of the testing circuit to the repeater to testthe ringing apparatus associated therewith. In order that the repeatermay be balanced with respect to the line simulating net works N and N orthe equivalent net works N,,' and N test net works N and N," areassociated with the balancing circuits 13 and 14, and the circuit is soarranged that when the plugs l, and P are inserted in the jacks J and Jof the testing trunks 15 and 16 and the repeater controllingkey 12operated, the test net works N, and N are automatically connected to thebalancing circuits by means of a selecting circuit similar to that forelecting the other balancing net works. In order to determine, whetheror not the operation of selecting the net work is properly performed,the key K is so arranged that when thrown to the right the test networks N and N will be disconnected. Upon restoring the. key K, to normalthe process of selecting these net works is again repeated and bylistening in over the monitoring circuit 19, which is connected to theoperators receiver by means of conductors 20, it may bedeterminedwhether eration which is as follows:' Assuming that a call hascome in over the line L the operator inserts the plug P in the jack Jthereby completing a circuit from" round through the winding of relay21, win ing of marginal relay 22, sleeve. contacts of the jack and plug,and through the winding of sleeve relay 23, in parallel withnoninductive resistance 25, andthence through resistance 24:" tobattery; Relays 21 and 23 are operated over this circuit but marginalrelay 22 is not actuated. Relay 23 completes a circuit overitsleft handfront eontaets from ground, through the winding of relay 24 which isthereby energized. Relay 24 completes a circuit from battery through thewinding of relay 25, back contacts of ringing responsive relays 26 and27 and over the upper front contact of relay 24 to ground. Relay 25 uponbeing energized holds open the circuit which would otherwise be closedfrom ground over the upper front contact of relay 24:, contact of relay25, and through the winding of relay 28. The purpose of the relays 25and 28 is to control the actuation of the ringing signal as hereinafterdescribed. l

, Since the plug P is normally connected with the cord circuit '9, theoperator by actuating key 10 may bridge her telephone set across thecord circuit 9 by meansof concontact of relay 34, upper make contact ofkey 12, and through the winding of relay 35 to battery. Relay 35connects battery 36 to the filaments of amplifiers A, and A therebyrendering the amplifier tubes operative. Upon operating the repeatercontrolling key 12 a circuit is also completed from battery over thelower back contact of relay 37, right hand front contact of relay 23,

left hand front contact ofrelay 31, lower make contact of key 12, lowerback contact of relay 38, through the winding of the relay Rcorresponding to the repeater now be1ng described, and thence in seriesover the right hand back contacts of slmilar relays R, R, etc., of otherrepeaters to ground. It will be seen-that this circuit is so, arrangedthat if the R relay of any other repeater is operated the circuits ofall other H relays are held open thereby preventing selection by otherrepeaters. The R relays are maintained energized only during the briefperiod required for selecting a net work and consequently the R relay ofno other repeater can be energized until the repeater which is at thatmoment selecting has completed the selection of its net work.

As soon as the circuit just described for the relay R is complete saidrelay is energized and at its two right hand contacts opens the initialenergizing circuits for the R relays of all other repeaters. At itsinner right hand front contact relay R completes a circuit from batteryover said contact, over the back contact of relay 39, left hand frontcontact of relay B, through the winding of sleeve relay 23, sleevecontacts of the plugQP and ack J and through the windings of relays 22and 21 to ground.

Since battery is connected directly through the winding of sleeve relay23 to the winding of marginal relay 22 over the circuit above described,marginal relay 22 is energized and over its front contacts connects theground to the various selecting circuits for selecting basic net works,composite balancing net works, phanton balancing net works, etc. Asillustrated, selecting circuits for the basic net work N and compositebalancing net work N only are shown.

Returning to the relay R battery is connected over the inner right handfront contact of said relay, over the upper back contact of relay 37,and over conductor 40, and

thence in parallel through the windingof relays 41, 42, etc. Battery. isalso applied over the inner right hand front contact of relay R andupper back contact of relay 37 through the winding of relay 43 toconductor 44. Relays 41, 42, etc., upon being energized, connect batteryfrom conductor 44 to the various selecting circuits. Consequently acircuit is completed from battery over the inner right hand frontcontact of relay R, upper back contact of relay 37, winding of relay 43,conductor 44 and thence in parallel through the front contacts of relay41,

lower back contacts ofselectingrelays 45 and 46, through the windingsand upper back contacts of said relays and over the contacts of relay 22to ground. Selectin relay 39, resistance 47, conductor 48, anc over thecircuit just described, the latter relay functioning to close ashort-circuit about the relay 39 to prevent the energization of saidrelay. Relays 45 and open their initial energizing circuits, therebydeenergizing the relay 43 and completing locking circuits from batteryover the inner right hand front contact of relay B, through the windingof relay 39, resistance 47,-conductor 48, and thence in parallel overthe lower front contacts of relays 45 and 46, through the windings andupper front contacts ofsaid relays, to ground. Relay 45 at its upperfront contact completes a circuit from ground through the windings of relays 49 and 50 to battery. Relay 49 opens the direct connection betweenthe two sections of balancing circuit 13 and relay 15includ'es'therein}; the composite balancing net work N Relay 46 'at itsupper front contacts connects the basic line balancing net work N, tothe balancing circuit13.

Returning to the relay 39,said relay upon being energized opens thedirect battery connection previously traced over its lowerback contactto the sleeve circuit, thereby causing the marginal relay 22 to bedenergized.

Relay 22 upon being deenergized disconi nects ground from the variousselecting circuits. Relay 39 at its lower front contact completes acircuit frombattery over the inner right hand front contact of relay Rand over the front contact of relay 39, through the winding of relay 37to ground. Relay 37 upon being energized at its lower front contactestablishes a new circuit for the relay R from battery over the lowerfront 46, upon being energized,

contact of relay 37, right hand front contact of relay 23, left handfront contact of relay 31, lower make contact of repeater controllingkey 12, lower back contact of relay 38 and thence through the winding ofrelay R to ground over the circuit previously traced. 7

At its middle front contact relay 37 applies battery' directly to thesleeve circuit of plug P and jack J, as follows: from battery over theinner right hand front contact of relay R, middle front contact of relay37, lower back contact of relay 49 through the winding of rela 31,sleeve contact of plug P and jack 1 through the winding of marginalrelay and the winding of relay 29 to ground. Marginal relay 30 is nowenergized and applies ground to the various selecting circuitsassociated with the right hand side of the repeater.

A circuit is completed over the upper front contact of relay 37 frombattery, inner right hand front contact of relay R, upper front contactof relay 37, middle back contact of relay 38, conductor 50 and throughthe windings of relays 51, 52, etc., in parallel to ground. Relays 51,52, etc., upon being energized apply battery to the various selectingcircuits so that selecting circuits are completed over the contacts ofrelay 51 as follows: from battery, inner right hand front contact ofrelay R, upper front contact of relay 37, middle back contact of relay38, winding of relay 53, conductor 54, and thence in parallel over thefront contacts of relay 51, lower back contacts of relay 55 and 56,windings and up- I per back contacts of said relays, front right handcontacts of marginal relay 30, to

ground. Relays 53, 55 and 56 are energized over the circuit abovetraced, the former relay at its lower front contact completing ashort-cicrcuit about the winding of relay 49 to prevent the energizationof said relay. Relays 55 and 56, upon being energized, open the circuitjust traced through the windings of relay 53, which relay isdeenergized, and opens the shortcircuit about the winding of relay 49.Looking circuits for relays 55 and 56 are completed from battery overthe inner right hand front contact of relay R, upper front contact ofrelay 37, middle back contact of relay 38, winding of relay 49,resistance 57, conductor 58 and thence in parallel over the lower frontcontacts, windings and upper front contacts of relays .55 and 56 toground.

Relay 55 at its upper contact completes a circuit for relays 59 and 60,the former of which opens the direct connection between the two sectionsof balancing circuit 14, and the latter of which includes the balancingnet work N between the two sections. Relay 56 at its upper frontcontacts connects balancing net work N, to the balancing circuit 14.

Relay 49, upon being energized, disconnects the direct batteryconnection from the sleeve circuit,thereby de'c'nergizing marginal relay30, which removes the ground from the selecting circuits. At its lowerfront contact relay 49 completes'a circuit for the relay 38 frombattery, inner right hand front contact of relay R, middle front contactof relay 37,1ower front contact of relay 49, winding of relay 38, toground.

Relay 38, upon being energized, at its lower contact, opens the holdingcircuit for the relay R which is now deenergized, thereby permittingother repeaters to select, if they r of relay 39 and through the windingof relay 37 to ground, through the winding of relay 39, resistance 47,conductor 48, and over the holding circuits of relays 45 and 46 toground, over the upper front contact of relay 37 winding of relay 49,resistance 57, conductor 58, and over the locking circuits of relays 55and 56- to ground, and over the middle front contact of relay 37, lowerfront contactof relay 49 and winding of relay 38 to ground These lockingcircuits will now be maintained so long as the sleeve relays 23' and 31are energized and the repeater controlling key 12 remains actuated.

Relay 38, by opening its middleback contact, disconnects battery fromconductors 50 and 54, thereby deenergizing" relays 51, 52, etc., torestore the initial energizing circuits of the selecting'relays tonormal. Relay 38 at its upper front contact completes a circuit asfollows: from ground, over the upper ings of relays 64 and 65, tobattery. Relays 65 disconnect the plugs P and P from the cord circuit 9and connect the plugs directly to the circuits of the amplifiers A,and-A While relay 62 opens the short-circuits normally'existing acrossthe input circuits of the amplifiers, thereby rendering the repeatercircuits 0 erative. The transmission lines L and J2 are nowinterconnected through the repeater which is balanced by net worksconforming to the requirements of these transmission lines andtransmission may take place over the circuit. 7 Should a rlnging signalbe transmitte over one of the transmiss on lines, as for instance, lineL ringing responsive relay 26 will be actuated, thereby opening thecircuit of relay 25. Relay 25 is slightly slowacting and after aninterval completes a circuit for relay 28 from battery, through thewinding of said relay, back contact of relay 25, and

over the upper front contacts of relays 24 and 34 to ground. Relay 28 atits left hand front contact completes a circuit for relay 66 frombattery, through the winding of said relay, left hand front contact ofrelay 28, and over the upper front contacts of relays 24 and 34 toground. Relay 66 completes a locking circuit from battery, through itswlnding, and over its left hand front contact, over the lower contact oflistening key 10, and over the upper front contacts of relays 24 and 34to ground. At its right hand front contact, relay 66 completes a circuitfor signal lamp 6'? to apprise the operator of the fact that a ringingsignal has come in.

clay 28, at its right hand front contact,

I completes a circuit for relay 63, from battery, winding of said relay,right hand front contact of relay 28, upper front contact of relay 38,lower front contact of relay 34, lower front contact of relay 24, uppercontact of listening key 10, and over the upper front contacts of relays24 and 34 to ground. Relay 63, at its left hand front contact, completesa holding circuit for relays 64 and 65, and at the same time opens thecircuit of relay 62 which again short-circuits the input circuits of theamplifiers A, and A, to prevent ringing current from being transmittedto the amplifiers.

The operator, upon observing the glowing of the signal lamp 67 actuatesthe listening keylO which, at its lower contact, opens the lockingcircuit of relay 66, thereby extinguishing the lamp 67. As soon as theringing current ceases, relay 25 is again energized, thereby opening thecircuit of relay 28, which in turn opens the circuit of relay 63. Thecircuit ofrelay 63 is also opened at the upper contact of the listeningkey 10. The circuits of relays 62, 64'and 65 are also opened at theupper contact of the listening key 10 so that the plugs P and P aredisconnected from the repeater and again connected to the cord circuit9, the relay 62 at the same time maintaining the input circuits of therepeater short-circuited. The operators set is now bridged across thecord circuit and she may listen in upon the connection. As soon as sherestores the listening key 10 to normal, the circuits of relays 62, 64and 65 are again completed over the upper contact of said key and therepeater is again connected into the transmission circuit.

Upontaking downthe connection, relays 23 and 31 are deenergized whentheplugs P and P are withdrawn from the jacks. These relays, at their righthand and left hand contacts respectively, open the holding circuitpreviously traced for relays 37 39, 49 and 38, which are thereuponrestored to normal. Selecting relays 45, 46, 55 and 567are restored tonormal at the same ime, thereby disconnecting the balancing net worksfrom the balancing circuits of the repeater. Relays 23 and 31, at theirleft hand and right hand contacts respectively, open the circuits ofrelays 24 and 34. Relays 24 and 34 open the circuits of relays 35, 62,64, 65 and 25 so that the repeater apparatus is all restored to normalready for a new connection.

If it is desired to test the repeater circuits shown in Fig. 1 by meansof the testing circuit illustrated in Fig. 2, the plugs P and P of thetesting circuit are inserted in the jacks J, and J of testing trunks l5and 16, while the plugs P and P of the repeater are inserted in thejacks J J of said trunks. Relays 23 and 31 are energized over the sleevecircuits of the jacks J and J 22 their circuits being extended tomarginal relays 68 and 69 respectively. Relays 68 and 69 are notenergized, however, because of the resistance included in the sleevecircuits. Relays 23 and 31 energize relays 24 and 34 over circuitsalready described. Relays 24 and 34 in turn complete a circuit for therelay 25 over the contacts of theringing responsive relays 26 and 27 Theoperator at the switchboard by actuating the repeater controlling keycompletes circuits whereby the filaments of the amplifiers areenergized, net works are selected to balance the repeater, and the plugsP and 1 are disconnected from the cord circuit and connected to therepeater. Since these circuits are, for the most part, identical withthe circuits previously described in connection with the setting up of aregular connection, they need not be described in detail and only thefeatures which are different will be pointed out.

It will be noted that the plugs P and P are connected to net works N andN in the testing circuit, these net works being designed to simulate thecharacteristics of the transmission lines with which the repeater isordinarily used. It is necessary that these net works be balanced'withrespect to the reeater and for this purpose test net works and N areprovided, the selecting circuit being so arranged that thesevtest networks are selected instead of the usual balancin net works. 'It will beremembered that the actuation of the repeater controlling key completeda circuit for the relay R of the repeater, which in turn applied batterydirectly to the sleeve circuit through the relay 23. .Marginal relay 68is there fore energized and connects ground to the circuit for the.selectingjrelay 70 is completed from battery over a circuit pre viouslytraced, to the winding'of relay 43, through the winding of said relay,over conductor 44, front contacts of relay 42, lower A back contact,winding and upper back 0011- tact of relay 70, and left hand frontcontact of relay 68, to ground.

Relay 70 is now energized, opening the circuit of relay 43 andcompleting a locking circuit over its front contacts, over conductor 48,and through the winding of relay 39, to battery, over a circuitpreviously traced. Relay 70, at its upper front contacts, connects thetest net work N to the balancing circuit 13. Relay 39 opens the directbattery connection to the sleeve circuit, so that relay 68 isdeenergized, at the same time completing the circuit of relay 37.Battery is now connected directly to the sleeve of the jack J therebyenergizing marginal relay 69 which connects ground to the selectingcircuits. Battery is also applied to conductors 50 and 54 over circuitsalready traced, thereby energizing the relays 51, 52, etc. A selectingcircuit is now completed from battery, through the winding of relay 53,over the conductor 54, front contacts of relay 52, lower back contact,winding and upper back contact of relay 71, over the right hand frontcontact of relay 69 to ground. Relay 71 now opens its initial energizingcircuit through relay 53 and completes a locking circuit over theconductor 58 and through the winding of relay 49 to battery, over acircuit previously traced. At its upper front contacts relay 71 connectsthe test net work N to the balancing circuit 14. Relay 49 disconnectsthe direct battery connection from the sleeve circuit, therebydeenergizing relay 69, and completes a circuit previously traced fortherelay 38. The circuits whereby the relays 37 39, 49 and 38 are lockedup, and whereby the re peater is rendered o erative and connected to theplugs P and 2 are similar to those previously traced and need not befurther described. V

In order to make a transmission test, the key K of the testing circuitmay be thrown to the left, thereby completing a circuit from ground,over its upper left hand make contact and through the winding of relay72, to battery. Relay 72 sets the generator 16 into operation. The key Kmay also be thrownto the left, completing circuits for relays 74 and 75over its upper and lower make contacts and opening the shunt element 76and. short-circuiting the series element 77 of the receiver shunt 17.Relays 7 4 and 75 at. their upper contacts disconnect the testingcircuit from the repeater and interconnect the terminal conductors 78and 79 of the testing circuit, through the auxiliary path 18. Over thelower front contacts of relays 74 and 75, said relays connect auxiliarynet works N and N to the repeater circuit 'to maintain its balance whileing of ringing responsive relay 26.

mal contacts of key K conductors 81, right I hand normal contacts of keyK conductors 82, and conductors 83 to the receiver. The tone transmittedover this circuit having been observed by the operator, the key K willbe restored to normal, thereby de'elnergizing relays 74 and 75 toconnect the repeater to the testing circuit and removing theshortcircuit from the series element 77 of the receiver shunt, at thesame time bridgin shunt element 76 across the receiver circult. The toneis now transmitted over the circuit previously traced to conductors 78of the testing circuit and thence over the normal contacts of relay 74,tip contacts of plug conductors of jack J and plug P over the frontcontacts of relay 65, input circuit 3 of amplifier A through theamplifier, over the output circuit 5 of the amplifier, throughthe'induction coil 2, where the energy is divided, half beingtransmitted through the balancing circuit 14 and the other half beingtransmitted over the front contacts of relay. 64, tip and ring contactsof plug P andjack J conductors 16, tip contacts of jack J and plug Pupper back contacts of relay 75, conductors 7 9,'net work N conductors80, normal right hand contacts of key K conductors 81, normal right handcontacts of key K conductors 82, through the receiver shunt 17 and overconductors 83, to the receiver. The receiver shunt 17 may now be sametone is heard in the receiver as in the case of the previous circuit.The transmission loss due to the receiver shunt 17 is now equal to thegain due to the repeater and if the receiver shunt is calibrated interms of some suitable unit, the gain due to the repeater may be readdirectl In a similar manner, by throwing key I8; tothe right, a test maybe made for transmission in.,the opposite direction, through theamplifier A If it is desired to test the rin ing equip ment of therepeater, the key k may be thrown either to the right or to the left. Ifthrown to the left, ringing current will be applied over a circuitthrough the net-work N over conductors 78, upper back contacts of relay74,'tip contacts of plug P and ack J conductors 15, tip and ringcontacts of jack J and plug P to the wind The ringing responsive relay,upon being actuated, sets the same succession of circuits intooperation, whereby the lamp 67 is caused to glow, as already described.The glowing of the lamp 67 indicates that the ringing apparatus isfunctioning properly." When ever the key K is actuated a circuit iscompleted over the lower contact'of said key for a relay which operatesto change the value 01 the shunt impedance of the networks N N This isdone for the purpose of changing the impedance of the circuit to'a valuesimulating that of an ordinary transmission line for low frequencyringing current. As this feature forms no part of the. present inventionit need not be described in further detail.

If it is desired to test the net work selecting equipment in order todetermine whether or not it is operating satisfactorily, the key K, maybe thrown to the right, thereby completing a circuit over the sleevecontacts of plug P, and jack J andthrough the winding of relay 85, Relay85 opens the sleeve'circuit through the relay 23 of the repeater,thereby deenergizing said relay which in turn deenergizes the relay 24.iRelayv 23, at its right hand contact, opens the locking circuits forrelays 37, 39, Q9 and 38 which are restored to normal, therebydeenergizing selecting relays 7 0 and 71 so that the test net works aredisconnected from the balancing circuits. Relay 2d, at its" lowercontact, opens the circuit for relays 62, 64 and 65, therebydisconnecting the repeater from the plugs P and P and r ndering therepeater inoperative. As soon as the key K is restored, however, therelay 85 is de'einergized, thereby again closing the sleeve circuit andenergizing relay 23, whereupon the operation of selecting the test networks is again repeated. The operator may listen in by means of herreceiver,

which isconnected'over conductors 20 to the monitoring c1rcu1t 19, todetermine whether this operation is performed without the repeatersinging and without undue clicks or inductive disturbances. operationthus observed not be satisfactory, a defect in the circuit is indicatedwhich should be given attention. V

It will be seen that by means of the arrangements above described asimple and efiicient means is provided for making the usual routinetransmission test of cord cir- V cuit repeaters and in addition theretotesting the net work selecting equipment. Furthermore it will beobviousthat the general principle herein disclosed .may be embodied inmany other organizations widely different from thoseillustrated,"without departing from the spirit of the invention, asdefined in the following claims.

What is claimed is:

1 In a signaling system, transmission line sections, a repeater forinterconnecting said sections,-a testing circuit for said repeaterincluding networks for simulating the characteristics of line sectionswith Should the.

which the repeater is ordinarily used, artificial lines associated withsaid repeater for balancing said networks, means to disconnect saidtesting circuit and netwo ks from said repeater and to associate themwith an auxiliary path, and means to associate auxiliary balancing meanswith said repeater to maintain the repeater balanced while the testingcircuit and net works are associated with said auxiliary path.

2. In a signaling system, transmission line sections, a repeater forinterconnecting said sections, a testing circuit for said repeaterincluding net works for simulating the characteristics of line sectionswith which the repeater is ordinarily used, artificial lines associatedwith said repeater for balancing said net works, a. source of currentvariations and an indicating means associated with said testing circuit,switching means whereby current from said source 'may be transmitted tosaid testing circuit and through said net works and said repeater tosa1dlndicatlng means, an auxil- 1ary path, switching means whereby saidtesting circuit andfnet works may be dis-,

connected from said repeater and associated with said auxiliary path sothat current from said source may be transmitted through said net worksand over-said path to the indicating means, and means'to associateauxiliary balancing means with said repeater to maintain therepeaterbalanced whilev the testing circuit and net works are associated withsaid auxiliary path.

3. In a signaling system, a repeater, balancing net works'associatedtherewith for balancing said repeater with respect to line sections withwhich it is associated, test net works associated with said repeater,auto matic net work selecting means associated with said repeater, atesting circuit, means to associate said repeater with said testingcircuit, means responsive to the association of said repeater with saidtesting circuit to cause said selecting means to select said test networks, and means associated with said testing circuit to test theoperation of said selecting means.

4. In a signaling system, a repeater, balancing net works associatedtherewith, auto matic net work selecting means also associ-.

ated with said repeater, a testing' circuit, means to associate saidrepeater with said testing circuit, and means operative upon theassociation of said repeater with said testing circuit to cause saidselecting means the association of said repeater with said testingcircuit to cause said selecting means to select balancingnet works for.the repeater and means to test the operation of selecting net works.

6. In a signaling system, a repeater, balancing net works associatedtherewith for balancing said repeater with respect to line sections withwhich it is associated, test net works associated with said repeater,.auto- 'matic net work selecting means associated with said repeater, atesting circuit, means to associate said repeater Wltll SiLlCl testingcircuit, means responsive to the association of said repeater with saidtesting circuit to cause said selecting means to select said test networks, means associated with said testing circuit to restore theselecting means to normal and thereafter cause the selecting operationsto be repeated, and means toobserve the selecting operation, I

In testimony whereof I have signed my name to this specification thisfourth day of December, 1918.

CHARLES s. DEMAREST.

